The present invention relates to an X-ray radiographic apparatus, in particular, to the X-ray radiographic apparatus incorporating an optical camera for obtaining a surface image of an object being imaged, the optical camera being arranged in an X-ray beam limiting device for limiting X-ray beams radiating from an X-ray tube toward the object.
In X-ray radiography, there are two radiographic methods; one is a direct radiographic method by which an X-ray image can be obtained by exposing transmitted X-rays through an object body onto an X-ray film, while the other is an indirect radiographic method by which transmitted X-rays are converted by an image intensifier (I.I.) into visible light rays received by a TV camera to obtain an X-ray image. An X-ray radiographic apparatus employing such methods has been widely used in examinations of digestive tracts and bronchial tubes using contrast medium and other examinations.
An X-ray radiographic apparatus comprises an X-ray tube radiating X-ray beams and an X-ray beam limiting device limiting the X-ray beams from the X-ray tube for avoiding excess X-ray exposure. The X-ray beam limiting device incorporates a set of limiting blades forming an aperture for X-ray beams. Thus, adjusting the size of the aperture permits an X-ray radiation field to be specified into a desired size on the object.
FIG. 1 shows a conventionally used X-ray radiographic apparatus 1 having an X-ray tube 2 and an X-ray beam limiting device 3. In the limiting device 3, a lamp 4 is disposed at a position that is conjugate to an X-ray focal point FP of the X-ray tube 2. As shown in the figure, X-ray beams radiated from the focal point FP of the X-ray tube 2 reaches a patient P lain on a tabletop 5 of a patient couch.
Lighting up the lamp 4 allows its light rays to reflect on a mirror 6 and then to radiate onto the object P, so that a light radiation field from the lamp 4 is coincident with an X-ray radiation field.
Accordingly, prior to X-ray exposure in X-ray examination, the X-ray radiation field is known to an operator by lighting up the lamp 4. Therefore, in normal conditions, the operator has used the light radiation field to adjust the aperture of a limiting member 3a incorporated in the X-ray beam limiting device 3 and to adjust relative positional relation among the X-ray tube 2, the patient P, and X-ray beam receiving devices such as an X-ray film 7 (or cassette or image intensifier).
However, when the above X-ray radiographic apparatus is used, it is required that the radiographic room be rather dark to confirm the light radiation field (i.e., X-ray radiation field) of the lamp. The darker room requires not only much operation time for the above-mentioned various adjustments but skilled operation techniques. These drawbacks are enhanced in mass screening, thereby causing a longer examination time in mass screening.
In case that the head portion of a patient is examined, dazzling light beams fall into the patient's eyes, imposing considerable endurance on the patient.
Further, when considering the longevity of the lamp, it is preferred to avoid lighting up the lamp for a longer period of time at one time. However, a shorter operation time sometimes causes an operator to be inconvenient for obtaining a highly accurate aperture of the X-ray limiting member.
Still further, fluoroscopy using a small quantity of X-ray may be carried out in the above-mentioned indirect radiography employing an image intensifier. In such a case, the aperture of an X-ray limiting device is sometimes adjusted with a fluoroscopy image. This results in an excessive X-ray exposure to a patient.
On the other hand, the above-mentioned drawbacks are also true in stereoradiography that uses an X-ray tube having a pair of X-ray focal points therein.